Lubricating composition

ABSTRACT

A lubricating oil composition comprising:
     (a) a base oil composition comprising Fischer-Tropsch derived base oil; and   (b) an organic molybdenum compound;   (c) 30 wt % or less solvency booster;   (d) antioxidant selected from aminic antioxidants, phenolic antioxidants, and mixtures thereof;   (e) detergent comprising alkaline earth metal salicylate.   

     The lubricating oil composition of the present invention provides improved anti-wear properties, as well as improved oxidation and improved piston cleanliness properties.

FIELD OF THE INVENTION

The present invention relates to a lubricating composition, in particular a lubricating composition having improved anti-wear performance.

BACKGROUND OF THE INVENTION

Lubricating oils are used in internal combustion engines, gearboxes and other mechanical devices to promote smoother functioning. Internal combustion engine lubricating oils (engine oils), in particular, must exhibit a high level of performance under the high-performance, high-output and harsh operating conditions of internal combustion engines. Various additives such as anti-wear agents, metal cleaning agents, non-ash powders and antioxdiants are therefore added to conventional engine oils to meet such performance demands. The fuel efficiency performance required of lubricating oils has continued to increase in recent years, and this has led to application of various high viscosity-index base oils or friction modifiers. Various friction modifier/anti-wear additives are known for use in lubricating compositions for providing acceptable anti-wear performance. Examples of known anti-wear additives include zinc dithiophosphate compounds selected from zinc dialkyl-, diaryl- and/or alkylaryl-dithiophosphates, molybdenum-containing compounds, and ashless anti-wear additives such as substituted or unsubstituted thiophosphoric acids, and salts thereof.

However, as the demand for ever improving lubricating performance increases, there is a need for developing lubricating compositions having improved anti-wear performance.

SUMMARY OF THE INVENTION

According to the present invention there is provided a lubricating oil composition comprising:

(a) a base oil composition comprising a Fischer-Tropsch derived base oil; and

(b) an organic molybdenum compound;

(c) 30 wt % or less solvency booster;

(d) antioxidant selected from aminic antioxidants, phenolic antioxidants, and mixtures thereof;

(e) detergent comprising alkaline earth metal salicylate.

According to another aspect of the present invention there is provided the use of a lubricating oil composition comprising:

-   -   (a) a base oil composition comprising Fischer-Tropsch derived         base oil; and     -   (b) an organic molybdenum compound;     -   (c) 30 wt % or less solvency booster;     -   (d) antioxidant selected from aminic antioxidants, phenolic         antioxidants, and mixtures thereof;     -   (e) detergent comprising alkaline earth metal salicylate;         for providing improved anti-wear performance.

It has surprisingly been found that the combination of a Fischer-Tropsch derived base oil together with a molybdenum-containing organic compound in a lubricating composition also comprising 30 wt % or less solvency booster, antioxidant and alkaline earth metal salicylate provides improved anti-wear performance, together with improved oxidation stability and reduced deposits.

DETAILED DESCRIPTION OF THE INVENTION

The lubricating composition of the present invention comprises a base oil composition. The base oil composition comprises a Fischer-Tropsch derived base oil.

Fischer-Tropsch derived base oils are known in the art. By the term “Fischer-Tropsch derived” is meant that a base oil is, or is derived from, a synthesis product of a Fischer-Tropsch process. A Fischer-Tropsch derived base oil may also be referred to as a GTL (Gas-To-Liquids) base oil. Suitable Fischer-Tropsch derived base oils that may be conveniently used as the base oil in the lubricating composition of the present invention are those as for example disclosed in EP 0 776 959, EP 0 668 342, WO 97/21788, WO 00/15736, WO 00/14188, WO 00/14187, WO 00/14183, WO 00/14179, WO 00/08115, WO 99/41332, EP 1 029 029, WO 01/18156 and WO 01/57166.

Typically, the aromatics content of a Fischer-Tropsch derived base oil, suitably determined by ASTM D 4629, will typically be below 1 wt. %, preferably below 0.5 wt. % and more preferably below 0.1 wt. %. Suitably, the base oil has a total paraffin content of at least 80 wt. %, preferably at least 85, more preferably at least 90, yet more preferably at least 95 and most preferably at least 99 wt. %. It suitably has a saturates content (as measured by IP-368) of greater than 98 wt. %. Preferably the saturates content of the base oil is greater than 99 wt. %, more preferably greater than 99.5 wt. %. It further preferably has a maximum n-paraffin content of 0.5 wt. %. The Fischer-Tropsch derived base oil preferably also has a content of naphthenic compounds of from 0 to less than 20 wt. %, more preferably of from 0.5 to 10 wt. %.

Typically, the Fischer-Tropsch derived base oil or base oil blend has a kinematic viscosity at 100° C. (as measured by ASTM D 7042) in the range of from 1 to 35 mm²/s (cSt), preferably from 1 to 25 mm²/s (cSt), more preferably from 2 mm²/s to 12 mm²/s. Preferably, the Fischer-Tropsch derived base oil has a kinematic viscosity at 100° C. (as measured by ASTM D 7042) of at least 2.5 mm²/s more preferably at least 3.0 mm²/s. In one embodiment of the present invention, the Fischer-Tropsch derived base oil has a kinematic viscosity at 100° C. of at most 5.0 mm²/s, preferably at most 4.5 mm²/s, more preferably at most 4.2 mm²/s (e.g. “GTL 4”). In another embodiment of the present invention, the Fischer-Tropsch derived base oil has a kinematic viscosity at 100° C. of at most 8.5 mm²/s, preferably at most 8 mm²/s (e.g. “GTL 8”).

Further, the Fischer-Tropsch derived base oil typically has a kinematic viscosity at 40° C. (as measured by ASTM D 7042) of from 10 to 100 mm²/s (cSt), preferably from 15 to 50 mm²/s.

Also, the Fischer-Tropsch derived base oil preferably has a pour point (as measured according to ASTM D 5950) of below −30° C., more preferably below −40° C., and most preferably below −45° C.

The flash point (as measured by ASTM D92) of the Fischer-Tropsch derived base oil is preferably greater than 120° C., more preferably even greater than 140° C.

The Fischer-Tropsch derived base oil preferably has a viscosity index (according to ASTM D 2270) in the range of from 100 to 200. Preferably, the Fischer-Tropsch derived base oil has a viscosity index of at least 125, preferably 130. Also it is preferred that the viscosity index is below 180, preferably below 150.

In the event the Fischer-Tropsch derived base oil contains a blend of two or more Fischer-Tropsch derived base oils, the above values apply to the blend of the two or more Fischer-Tropsch derived base oils.

Preferably, the base oil composition contains more than 50 wt. %, preferably more than 60 wt. %, more preferably more than 70 wt. %, even more preferably more than 80 wt. %. most preferably more than 90 wt. % Fischer-Tropsch derived base oil, by weight of the base oil composition. In an especially preferred embodiment not more than 5 wt. %, preferably not more than 2 wt. %, of the base oil composition is not a Fischer-Tropsch derived base oil. It is even more preferred that 100 wt % of the base oil composition is based on one or more Fischer-Tropsch derived base oils.

Preferably the base oil composition comprising the Fischer-Tropsch derived base oil has a kinematic viscosity at 100° C. of between 2 and 35 cSt, preferably between 2 and 10.5 cSt (according to ASTM D 445).

In addition to the Fischer-Tropsch derived base oil, the lubricating composition may comprise one or more other types of mineral derived or synthetic base oils, including Group I, II, III, IV and V base oils according to the definitions of American Petroleum Institute (API). These API categories are defined in API Publication 1509, 15th Edition, Appendix E, July 2009.

The lubricating composition herein may comprise a PAO base oil in addition to the Fischer-Tropsch base oil. Poly-alpha olefin base oils (PAOs) and their manufacture are well known in the art. Preferred poly-alpha olefin base oils that may be used in the lubricating compositions of the present invention may be derived from linear C₂ to C₃₂, preferably C₆ to C₁₆, alpha olefins. Particularly preferred feedstocks for said poly-alpha olefins are 1-octene, 1-decene, 1-dodecene and 1-tetradecene.

The total amount of base oil incorporated in the lubricating composition of the present invention is preferably an amount in the range of from 60 to 99 wt. %, more preferably an amount in the range of from 65 to 90 wt. % and most preferably an amount in the range of from 70 to 85 wt. %, with respect to the total weight of the lubricating composition.

Another essential component of the lubricating oil compositions of the present invention is an organic molybdenum compound.

The organic molybdenum compound for use herein may be a sulphur-containing organic molybdenum compound such as molybdenum dithiophosphate or molybdenum dithiocarbamate.

The organic molybdenum compound is present in the lubricating composition preferably at a level of 0.001% by weight or greater, more preferably 0.005% by weight or greater, even more preferably 0.01% by weight of greater, and most preferably 0.02 wt % by weight or greater, in terms of the amount of elemental molybdenum based on the total weight of lubricating composition. The organic molybdenum compound is present in the lubricating composition preferably at a level of no greater than 1 wt %, more preferably no greater than 0.2 wt %, even more preferably no greater than 0.1% by weight, especially no greater than 0.07% by weight and most preferably no greater than 0.05 by weight, in terms of amount of elemental molybdenum based on the total weight of lubricating composition.

The lubricating composition may comprise a solvency booster. As used herein, the term “solvency booster” means a component which enhances the solvency of the Fischer-Tropsch derived base oil, for example as measured by improvement of deposit reduction properties, as measured by the TEOST test method (thermo-oxidation engine oil simulation test according to ASTM D7097-09) and the KHTT test method (Komatsu Hot Tube Test according to JPI-5S-55-99).

The solvency booster may be present at a level of 30 wt % or less, preferably 20 wt % of less, more preferably 15 wt % or less, by weight of the lubricating oil composition. The solvency booster may be present at a level of 1 wt % or more, more preferably 3 wt % or more, even more preferably 5 wt % or more, by weight of the lubricating oil composition.

Suitable solvency boosters for use herein are preferably selected from alkylated aromatic compounds, such as alkylated naphthalenes, naphthenic base oils and ester base oils, and mixtures thereof.

Preferred alkylated aromatic compounds for use as a solvency booster herein include alkylated benzenes, alkylated anthracenes, alkylated phenanthrenes, alkylated biphenyls, and alkylated naphthalenes and mixtures thereof.

Alkylated naphthalenes may be produced by any suitable means known in the art, from naphthalene itself or from substituted naphthalenes which may contain one or more short chain alkyl groups having up to about eight carbon atoms, such as methyl, ethyl, or propyl, etc. Suitable alkyl-substituted naphthalenes include alphamethylnaphthalene, dimethylnaphthalene, and ethylnaphthalene. Naphthalene itself is especially suitable since the resulting mono-alkylated products have better thermal and oxidative stability than the more highly alkylated materials. Suitable alkylated naphthalene lubricant compositions are described in U.S. Pat. No. 3,812,036, and U.S. Pat. No. 5,602,086. The preparation of alkylnaphthalenes is further disclosed in U.S. Pat. No. 4,714,794.

The alkylated aromatic compound for use herein is preferably selected from alkylbenzene compounds, alkylnaphthalene compounds, and mixtures thereof. The alkylaromatic component preferably has a kinematic viscosity at 100° C. in the range of from 3 to 12 mm²/s, more preferably in the range of from 3.8 to 7 mm²/s. Preferably the viscosity index of the alkylaromatic component is above 40, more preferably at or above 70.

An especially preferred alkylated aromatic compound for use herein is an alkylnaphthalene compound. Examples of commercially available alkylnaphthalene compounds are those available from King Industries under the tradename NA-Lube such as NA-Lube KR 008, NA-Lube KR019, and the like, and those available from ExxonMobil under the tradename Mobil MCP.

Examples of commercially available alkyl benzene include that available from Formasan under the tradename Fusyn-22, those available from Janex under the tradename Janex HAL, and those available from Shreive Chemical Products, Inc. (SCP) under the tradename ZEROL.

Suitable naphthenic base oils for use as a solvency booster herein includes naphthenic base oils having low viscosity index (VI) (generally 40-80) and a low pour point. Such base oils are produced from feedstocks rich in naphthenes and low in wax content. There is no particular limitation on the type of mineral-derived naphthenic base oil which can be used in the base oil composition herein. Any mineral-derived naphthenic base oil which is suitable for use in a lubricating oil composition can be used herein.

Naphthenic base oils are defined as Group V base oils according to API.

Such mineral-derived base oils are obtained by refinery processes starting from naphthenic crude feeds. Mineral-derived naphthenic base oils for use herein preferably have a pour point of below −20° C. and a viscosity index of below 70. Such base oils are produced from feedstocks rich in naphthenes and low in wax content. Mineral-derived naphthenic base oils are well known and described in more detail in “Lubricant base oil and wax processing”, Avilino Sequeira, Jr., Marcel Dekker, Inc, New York, 1994, ISBN 0-8247-9256-4, pages 28-35.

Methods of manufacture of naphthenic base oils can be found in “Lubricants and Lubrication (Second, Completely Revised and Extended Edition)”, published by Wiley-VCH Verlag GmbH & Co. KgaA, Chapter 4, pages 46-48.

An example of a suitable naphthenic base oil for use as a solvency booster herein is that commercially available from China National Petroleum Corporation under the tradename KN4006. Other examples of suitable naphthenic base oils for use as a solvency booster herein include those available from Calumet Specialty Products under the tradenames Hydrocal, Hydrosol and HR Tufflo, and those commercially available from Nynas Oil Company under the tradename Nynas.

Suitable esters for use as a solvency booster herein include natural and synthetic esters such as diesters and polyol esters. An example of a suitable ester for use as a solvency booster herein is the saturated polyol ester commercially available from Croda International PLC under the tradename Priolube 3970. Other suitable esters for use as a solvency booster herein include those available from Oleon under the tradename Radialube, those available from Emery under the tradename Emery and those available from ExxonMobil Chemical under the tradename Esterex.

The lubricating oil compositions of the present invention comprises a detergent which comprises an alkaline earth metal salicylate detergent. The lubricating oil compositions of the present invention preferably comprises from 0.01 wt % to 9 wt %, more preferably from 1 wt % to 6 wt %, even more preferably from 3.5 wt % to 5.5 wt o, of detergent, by weight of the lubricating oil composition.

In preferred embodiments herein, the lubricating oil compositions of the present invention comprise detergent, wherein the detergent comprises (i) an alkaline earth metal salicylate having a TBNE (total base number equivalent, as determined by ASTM D2896) in the range of from 50 to 150; (ii) an alkaline earth metal salicylate having a TBN in the range of from 150 to 250; and (iii) an alkaline earth metal salicylate having a TBN in the range of from 250 to 400.

It has been found that this particular combination of alkaline earth metal salicylates, together with the specified base oil, organic molybdenum compound, solvency booster and antioxidant has been found to especially helpful in providing improved oxidation stability and reduced deposits.

Suitable alkaline earth metal salicylates include calcium, magnesium and barium salicylates, and mixtures thereof, preferably calcium salicylates.

The level of an alkaline earth metal salicylate having a TBNE (total base number equivalent, as determined by ASTM D2896) in the range of from 50 to 150 is preferably in the range of 0.01 wt % to 5 wt %, more preferably from 1 wt % to 4 wt %, by weight of the lubricating oil composition.

The level of an alkaline earth metal salicylate having a TBN in the range of from 150 to 250 is preferably in the range of 0.01 wt % to 5 wt %, more preferably from 1 wt % to 3 wt %, by weight of the lubricating oil composition.

The level of alkaline earth metal salicylate having a TBN in the range of from 250 to 400 is preferably in the range of 0.01 wt % to 3 wt %, more preferably from 1 wt % to 2 wt %, by weight of the lubricating oil composition.

The lubricating oil compositions of the present invention comprises one or more anti-oxidants. Suitable anti-oxidants for use herein include phenolic antioxidants and/or aminic antioxidants.

Said antioxidants are preferably present in an amount in the range of from 0.1 to 5.0 wt. %, more preferably in an amount in the range of from 0.3 to 3.0 wt. %, and most preferably in an amount of in the range of from 0.5 to 1.5 wt. %, based on the total weight of the lubricating oil composition.

Examples of aminic antioxidants which may be conveniently used include alkylated diphenylamines, phenyl-α-naphthylamines, phenyl-β-naphthylamines and alkylated α-naphthylamines.

Preferred aminic antioxidants include dialkyldiphenylamines such as p,p′-dioctyl-diphenylamine, p,p′-di-α-methylbenzyl-diphenylamine and N-p-butylphenyl-N-p-′-octylphenylamine, monoalkyldiphenylamines such as mono-t-butyldiphenylamine and mono-octyldiphenylamine, bis(dialkylphenyl)amines such as di-(2,4-diethylphenyl)amine and di(2-ethyl-4-nonylphenyl)amine, alkylphenyl-1-naphthylamines such as octylphenyl-1-naphthylamine and n-t-dodecylphenyl-1-naphthylamine, 1-naphthylamine, arylnaphthylamines such as phenyl-1-naphthylamine, phenyl-2-naphthylamine, N-hexylphenyl-2-naphthylamine and N-octylphenyl-2-naphthylamine, phenylenediamines such as N,N′-diisopropyl-p-phenylenediamine and N,N′-diphenyl-p-phenylenediamine, and phenothiazines such as phenothiazine and 3,7-dioctylphenothiazine.

Preferred aminic antioxidants include those available under the following trade designations: “Sonoflex OD-3” (ex. Seiko Kagaku Co.), “Irganox L-57” (ex. Ciba Specialty Chemicals Co.) and phenothiazine (ex. Hodogaya Kagaku Co.).

Examples of phenolic antioxidants which may be conveniently used include C7-C9 branched alkyl esters of 3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy-benzenepropanoic acid, 2-t-butylphenol, 2-t-butyl-4-methylphenol, 2-t-butyl-5-methylphenol, 2,4-di-t-butylphenol, 2,4-dimethyl-6-t-butylphenol, 2-t-butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol, 2,5-di-t-butylhydroquinone, 2,6-di-t-butyl-4-alkylphenols such as 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol and 2,6-di-t-butyl-4-ethylphenol, 2,6-di-t-butyl-4-alkoxyphenols such as 2,6-di-t-butyl-4-methoxyphenol and 2,6-di-t-butyl-4-ethoxyphenol, 3,5-di-t-butyl-4-hydroxybenzylmercaptooctylacetate, alkyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionates such as n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, n-butyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and 2′-ethylhexyul-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,6-d-t-butyl-α-dimethylamino-p-cresol, 2,2′-methylene-bis(4-alkyl-6-t-butylphenol) such as 2,2′-methylenebis(4-methyl-6-t-butylphenol, and 2,2-methylenebis(4-ethyl-6-t-butylphenol), bisphenols such as 4,4′-butylidenebis(3-methyl-6-t-butylphenol, 4,4′-methylenebis(2,6-di-t-butylphenol), 4,4′-bis(2,6-di-t-butylphenol), 2,2-(di-p-hydroxyphenyl)propane, 2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane, 4,4′-cyclohexylidenebis(2,6-t-butylphenol), hexamethyleneglycol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], triethyleneglycolbis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate], 2,2′-thio-[diethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 3,9-bis{1,1-dimethyl-2-[3-(3-t-butyl-4-hydroxy-5-methyl-phenyl)propionyloxy]ethyl}2,4,8,10-tetraoxaspiro[5,5]undecane, 4,4′-thiobis(3-methyl-6-t-butylphenol) and 2,2′-thiobis(4,6-di-t-butylresorcinol), polyphenols such as tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, bis-[3,3′-bis(4′-hydroxy-3′-t-butylphenyl)butyric acid]glycol ester, 2-(3′,5′-di-t-butyl-4-hydroxyphenyl)methyl-4-(2″,4″-di-t-butyl-3″-hydroxyphenyl)methyl-6-t-butylphenol and 2,6-bis(2′-hydroxy-3′-t-butyl-5′-methylbenzyl)-4-methylphenol, and p-t-butylphenol-formaldehyde condensates and p-t-butylphenol-acetaldehyde condensates.

Preferred phenolic antioxidants include those available under the following trade designations: “Irganox L-135” (ex. Ciba Specialty Chemicals Co.), “Yoshinox SS” (ex. Yoshitomi Seiyaku Co.), “Antage W-400” (ex. Kawaguchi Kagaku Co.), “Antage W-500” (ex. Kawaguchi Kagaku Co.), “Antage W-300” (ex. Kawaguchi Kagaku Co.), “Irganox L-109” (ex. Ciba Speciality Chemicals Co.), “Tominox 917” (ex. Yoshitomi Seiyaku Co.), “Irganox L-115” (ex. Ciba Speciality Chemicals Co.), “Sumilizer GA80” (ex. Sumitomo Kagaku), “Antage RC” (ex. Kawaguchi Kagaku Co.), “Irganox L-101” (ex. Ciba Speciality Chemicals Co.), “Yoshinox 930” (ex. Yoshitomi Seiyaku Co.).

The lubricating oil composition of the present invention may comprise mixtures of one or more phenolic antioxidants with one or more aminic antioxidants. In addition to the components mentioned above, the lubricating composition according to the present invention may further comprise one or more additional additives such as anti-wear additives, anti-oxidants, dispersants, detergents, extreme-pressure additives, friction modifiers, viscosity index improvers, pour point depressants, metal passivators, corrosion inhibitors, demulsifiers, anti-foam agents, seal compatibility agents and additive diluent base oils, etc.

As the person skilled in the art is familiar with the above and other additives, these are not further discussed here in detail.

Specific examples of such additives are described in for example Kirk-Othmer Encyclopedia of Chemical Technology, third edition, volume 14, pages 477-526.

The above-mentioned additives are typically present in an amount in the range of from 0.01 to 35.0 wt. %, based on the total weight of the lubricating composition, preferably in an amount in the range of from 0.05 to 25.0 wt. %, more preferably from 0.1 to 20.0 wt. %, based on the total weight of the lubricating composition.

The lubricating composition may also comprise a viscosity modifier, preferably at a level of 30 wt % or less, based on the total weight of the lubricating composition. In one embodiment, the lubricating composition comprises from 20 wt % to 30 wt % of viscosity modifier. In another embodiment, the lubricating composition comprises 20 wt % or less of viscosity modifier. In a preferred embodiment of the present invention, the lubricating composition is essentially free of viscosity modifier. In a particularly preferred embodiment of the present invention, the lubricating composition comprises 0 wt % of a viscosity modifier.

Examples of viscosity index improvers include copolymers of alpha-olefins and dicarboxylic acid esters such as those described in U.S. Pat. No. 4,931,197. Commercially available copolymers of alpha-olefins and dicarboxylic acid diesters include the Ketjenlube polymer esters available from Italmatch (and previously Akzo Nobel Chemicals). Other suitable examples of viscosity index improvers are polyisobutylenes; commercially available polyisobutylenes include the Oloa (RTM) products available from Chevron Oronite.

Further examples of viscosity index improvers which may conveniently be used in the lubricating compositions of the present invention include the styrene-butadiene stellate copolymers, styrene-isoprene stellate copolymers and the polymethacrylate copolymers and ethylene-propylene copolymers (also known as olefin copolymers) of the crystalline and non-crystalline type.

Suitable olefin copolymers include those commercially available from Chevron Oronite Company LLC under the trade designation “PARATONE (RTM)” (such as “PARATONE (RTM) 8921” and “PARATONE (RTM) 8941”); those commercially available from Afton Chemical Corporation under the trade designation “HiTEC (RTM)” (such as “HiTEC (RTM) 5850B”); and those commercially available from The Lubrizol Corporation under the trade designation “Lubrizol (RTM) 7067C”. Suitable polyisoprene polymers include those commercially available from Infineum International Limited, e.g. under the trade designation “SV200”. Suitable diene-styrene copolymers include those commercially available from Infineum International Limited, e.g. under the trade designation “SV 260”.

In addition to the organic molybdenum compound, the compositions herein may include one or more further anti-wear additives. Suitable anti-wear additives for use herein include zinc dithiophosphate compounds selected from zinc dialkyl-, diaryl- and/or alkylaryl-dithiophosphates, and ashless anti-wear additives such as substituted or unsubstituted thiophosphoric acids, and salts thereof.

Examples of ashless thiophosphates are known in the art. These compounds are metal-free organic compounds. Suitable ashless thiophosphates for use in the lubricating oil composition of the present invention may include esters and/or salts of thiophosphoric acids, and substituted thiophosphoric acids. Preferably, the ashless thiophosphates are substituted by one or more hydrocarbyl groups which hydrocarbyl groups can optionally contain an acid, a hydroxy and/or an ester group. The hydrocarbyl moiety preferably is an alkyl group containing up to 12 carbon atoms. The hydrocarbyl-substituted thiophosphate preferably contains 2 or 3 hydrocarbyl groups, or is a mixture of thiophosphates containing 2 and 3 hydrocarbyl groups.

The ashless thiophosphates can contain any number of sulphur atoms directly linked to the phosphorus atom. Preferably, the thiophosphates are monothiophosphates and/or dithiophosphates.

Examples of ashless thiophosphates which may be conveniently used in the lubricating oil composition of the present invention are described in EP-A-0375324 , U.S. Pat. No. 5,922,657, U.S. Pat. No. 4,33,3841 and U.S. Pat. No. 5,093,016 and may be conveniently made according to the methods described therein.

Examples of commercially available ashless thiophosphates that may be conveniently used in the lubricating oil composition of the present invention include those available from Ciba Specialty Chemicals under the trade designations “IRGALUBE L-63” and “IRGALUBE 353” and that available from Lubrizol under the trade designation “LZ 5125”.

In a preferred embodiment, the lubricating composition comprises one or more anti-wear additives, preferably one or more zinc-based anti-wear additives, selected from one or more zinc dithiophosphates. The or each zinc dithiophosphate may be selected from zinc dialkyl-, diaryl- or alkylaryl-dithiophosphates.

Examples of zinc dithiophosphates which are commercially available include those available from Lubrizol Corporation under the trade designations “Lz 677A”, “Lz 1095”, “Lz 1097”, “Lz 1370”, “Lz 1371”, “Lz 1373” and “Lz 1395”, those available from Chevron Oronite under the trade designations “OLOA 260”, “OLOA 262”, “OLOA 267” and “OLOA 269R”, and those available from Afton Chemical under the trade designation “HITEC 7169” and “HITEC 7197”.

Preferably, the lubricating composition according to the present invention comprises a phosphorus containing compound, preferably selected from the group consisting of phosphonates, phosphates, phosphites, phosphorothionates and dithiophosphates, and combinations thereof. Examples of commercially available dithiophosphates and phosphates are “IRGALUBE 63” and IRGALUBE 349″, respectively, both available from Ciba Specialty Chemicals.

The lubricating oil composition of the present invention has a kinematic viscosity at 40° C. in the range of from 2 mm²/s to 220 mm²/s, preferably in the range of from 32 mm²/s to 220 mm²/s.

The lubricating compositions of the present invention may be conveniently prepared by admixing the one or more additives with the base oil(s).

The lubricating composition according to the present invention may be used in various applications, such as in internal combustion engines (as an engine oil), as a transmission oil, a grease, a hydraulic oil, an industrial gear oil, a turbine oil, a compressor oil, and the like.

In another aspect the present invention provides a method for improving anti-wear properties, which method comprises lubricating with a lubricating composition according to the invention. In another aspect, the present invention provides the use of a lubricating composition as described herein, for improving anti-wear properties (in particular as determined by ASTM G133 and/or the HFRR test method described hereinbelow).

The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the present invention in any way.

EXAMPLES Lubricating Oil Compositions

Various combinations of additives, base oils and friction modifiers were combined together to produce lubricating oil compositions. Table 1 shows the properties of the base oils. Table 2 indicates the amounts of additives, base oils and friction modifiers incorporated into the respective formulations; the amounts are given in wt. %, based on the total weight of the lubricating composition.

“Base oil 1” (or “B01” or “GTL 4”) was a Fischer-Tropsch derived base oil having a kinematic viscosity at 100° C. (ASTM D445) of approximately 3.89 cSt (M² s⁻¹). Base oil 1 may be conveniently manufactured by the process described in e.g. WO-A-02/070631, the teaching of which is hereby incorporated by reference.

“Base oil 2” (or “B02”) was a commercially available Group III base oil having a kinematic viscosity at 100° C. (ASTM D445) of approximately 4.3 cSt. Base oil 2 is commercially available from e.g. SK Energy (Ulsan, South Korea) under the trade designation “Yubase 4”.

TABLE 1 Base oil 1 Base oil 2 (GTL 4) (Yubase 4) Kinematic viscosity at 40° C.¹ [cSt] 16.91 19.49 Kinematic viscosity at 100° C.¹ [cSt] 3.89 4.3 VI Index² 127 126 Pour point³ [° C.] −39 −18 Noack volatility⁴ [wt. %] 11.2 14.2 Saturates⁵ [wt. %] 99.2 99.3 Tertiary Carbon, %⁶ 18.1 n.d. Secondary Carbon, %⁶ 66.7 n.d. Primary Carbon, %⁶ 14.3 n.d. Epsilon carbon content, %⁶ 12.1 n.d. n- and iso- paraffins⁷ 92.35 n.d. Mono-naphthenics⁷ 6.85 n.d. di- and poly- naphthenics⁷ 0.87 n.d. Aromatics⁵ 0.5 n.d. Dynamic viscosity at −20° C.⁸ [cP] n.d. 713 Dynamic viscosity at −25° C.⁸ [cP] n.d. 931 Dynamic viscosity at −30° C.⁸ [cP] 948 n.d. Dynamic viscosity at −35° C.⁸ [cP] 1580 n.d. ¹According to ASTM D 445 ²According to ASTM D 2270 ³According to ASTM D 5950 ⁴According to CEC L-40-A-93/ASTM D 5800 ⁵According to IP 368 (modified) ⁶According to 13C NMR ⁷According to FIMS ⁸According to ASTM D 5293 n.d. = not determined

HFFR Test

In order to measure the friction properties of the various lubricating compositions set out in Table 2, the lubricating compositions were subjected to the HFRR (high frequency reciprocating rig) test method as described in: Korcek, S., Jensen, R.K., Johnson, M.D., Sorab, J. “Fuel Efficient Engine Oils, Additive Interactions, Boundary Friction, and Wear.” Lubrication at the Frontier 1999, 13-24.

Improved friction properties (friction reduction) are evidenced by lower HFRR measured friction coefficients.

Sliding Wear Test Method

In order to measure the anti-wear properties of the various lubricating compositions set out in Table 2, the lubricating compositions were subjected to the sliding wear test method as per ASTM G133. Improved anti-wear properties are evidenced by a lower wear volume.

Table 2 lists additives and treat rates used in each formulation. Table 3 lists the HFRR measured friction coefficients and ASTM G133 wear volumes for each formulation tested.

TABLE 2 Concen- Additive tration Component Tradename Type (wt %) A1 Perfad FM-3338¹ Amide friction modifier 1 A2 Adeka FM-926² Amine friction modifier 1 A3 Sakura Lube S-515² Molybdenum 1 dialkyldithiocarbamate A4 Synative ES-2421³ Glycerol mono-oleate 1 A5 Infineum C9455⁴ Molybdenum 1 dialkyldithiocarbamate A6 Molyvan 822⁵ Molybdenum 1 dialkyldithiocarbamate A7 Priolube 3970¹ Ester 10 A8 Irganox L-57⁶ Diphenylamine 0.5 A9 Infineum M7102⁴ Calcium alkylsalicylate 1  A10 Infineum M7121⁴ Calcium alkylsalicylate 2  A11 Infineum M7125⁴ Calcium alkylsalicylate 0.5  A12 Infineum C9417⁴ Primary/secondary ZDDP 1 mixture In Table 2, the components marked with superscripts 1-6 are supplied by the following suppliers: ¹. supplied by Uniqema ². supplied by Adeka Corp. ³. supplied by Cognis Corp. ⁴. supplied by Infineum USA L.P. ⁵. supplied by R. T. Vanderbilt Co., Inc. ⁶. supplied by BASF

TABLE 3 HFRR Average μ_(F) ASTM G133 Wear Volume (μm³) Example Additive GTL 4 Yubase 4 GTL 4 Yubase 4  1* A1 0.122 0.124 522467 1170350  2* A1 + A7 + A8 + A9 + A10 + A11 + A12 0.104 0.111 856917 984883  3* A2 0.111 0.121 3569250 312391  4* A2 + A7 + A8 + A9 + A10 + A11 + A12 0.093 0.112 2404658 1516083  5 A3 0.068 0.080 1143433 2369933  6 A3 + A7 + A8 + A9 + A10 + A11 + A12 0.097 0.105 1333083 738367  7* A4 0.077 0.073 258258 188833  8* A4 + A7 + A8 + A9 + A10 + A11 + A12 0.090 0.096 1091300 849683  9 A5 0.124 0.117 Not measured Not measured 10 A5 + A7 + A8 + A9 + A10 + A11 0.131 0.115 115250 371583 11 A5 + A7 + A8 + A9 + A10 + A11 + A12 0.073 0.084 199333 300750 12 A6 0.231 0.233 Not measured Not measured 13 A6 + A7 + A8 + A9 + A10 + A11 0.137 0.136 251850 493283 14 A6 + A7 + A8 + A9 + A10 + A11 + A12 0.104 0.086 293333 759225 *Comparative Example

Discussion

The friction and wear performance of both GTL-based and mineral-based formulations is comparable, with the exception of formulations containing organic molybdenum-based friction modifiers (Examples 5, 10, 11, 13, 14) where, surprisingly, a trend towards lower wear is demonstrated in GTL.

The results presented herein demonstrate that formulations containing GTL base oil, organic molybdenum-based friction modifier and the indicated additives, namely, anti-oxidant, detergent, and solvency booster/co-solvent, permit improved wear protection (lower wear scars and lower wear volume) compared with mineral base oil-based formulations. 

1. A lubricating oil composition comprising: (a) a base oil composition comprising a Fischer-Tropsch derived base oil; and (b) an organic molybdenum compound; (c) 30 wt % or less solvency booster; (d) antioxidant selected from aminic antioxidants, phenolic antioxidants, and mixtures thereof; (e) detergent comprising alkaline earth metal salicylate.
 2. A lubricating oil composition according to claim 1 wherein the organic molybdenum compound is a sulphur-containing organic molybdenum compound.
 3. A lubricating oil composition according to claim 2 wherein the sulphur-containing organic molybdenum compound is selected from molybdenum dithiophosphate, molybdenum dithiocarbamate and mixtures thereof.
 4. A lubricating oil composition according to any of claims 1 to 3 wherein the detergent comprises (i) an alkaline earth metal salicylate having a TBNE (total base number equivalent, as determined by ASTM D2896) in the range of from 50 to 150; (ii) an alkaline earth metal salicylate having a TBNE in the range of from 150 to 250; and (iii) an alkaline earth metal salicylate having a TBNE in the range of from 250 to
 400. 5. A lubricating oil composition according to any of claims 1 to 4 wherein the solvency booster is selected from alkylated naphthalenes, alkyl benzenes, naphthenics, esters, and mixtures thereof.
 6. A lubricating oil composition according to any of claims 1 to 5 wherein the solvency booster is present at a level of from 1 wt % to 20 wt %, by weight of the lubricant composition.
 7. A lubricating oil composition according to any of claims 1 to 6, wherein the antioxidant is an aminic antioxidant, preferably a diphenylamine.
 8. A lubricating oil composition according to any of claims 1 to 7 wherein the alkaline earth metal salicylates are calcium salicylates.
 9. A lubricating oil composition according to any of claims 1 to 8 comprising one or more zinc-based anti-wear additives.
 10. A lubricating oil composition according to any of claims 1 to 9 wherein the Fischer-Tropsch derived base oil has a kinematic viscosity at 100° C. of from 1 mm²/s to 35 mm²/s.
 11. Use of a lubricating oil composition according to any of claims 1 to 10 for providing improved anti-wear properties, in particular as determined by the HFRR or the ASTM G133 sliding wear test method. 